Here are all 170 Plant Physiology questions asked in UPSC Agriculture Optional Paper II from 1995 to 2026, arranged under the 10 topics of the official syllabus. Within each topic the latest questions come first.
Each question ends with a code such as [2024/15m/3b] – the year, the marks, the word limit (where UPSC set one) and the question number in the paper.
4.1] Plant nutrition: absorption, translocation and metabolism of nutrients
16 questions
Describe the factors influencing nutrient absorption in plants from the soil. [2026/10m/150w/1c]
Classify plant mineral nutrients based on biochemical functions. How do excess minerals in the soil limit the plant growth? [2025/10m/150w/1e]
Discuss various theories of ion uptake with respect to passive absorption. [2024/10m/150w/1e]
Discuss the mechanisms of absorption and translocation of mineral nutrients in plants. [2022/20m/4a]
Enumerate factors responsible for absorption of nutrients by plants. Explain the mechanism of absorption of nutrients. [2020/10m/150w/1c]
Define plant nutrition. Give an account of essential and beneficial nutrients to plants and their status in Indian soils. [2020/20m/4a]
What makes a nutrient element become essential for plant growth and development? Which is the latest addition in the existing list of 16 essential plant nutrients? Mention its deficiency symptoms and functions. [2019/10m/150w/1c]
What are the different methods of diagnosis of mineral nutrient deficiency? Describe the role and deficiency symptoms of zinc in rice and sulphur in oilseed crops. [2018/10m/150w/5a]
Describe the criteria of essentiality of nutrients. Classify the essential nutrients for plants. Discuss the role of phosphorus and calcium in crops with special reference to pulses. [2017/10m/150w/5b]
Explain the mechanism of absorption of salts. Give potassium, calcium and iron deficiency symptoms in plants. [2016/10m/150w/1d]
Write the essential nutrients required by plants for growth and development. Explain the boron deficiency symptom in Cauliflower and Litchi. [2015/12.5m/4c]
The mechanisms of ion transport across membranes. [2013/10m/150w/5a]
Biochemical functions of N and K in plants. [2013/12.5m/200w/8a]
Khaira disease of rice. [2005/15m/8b]
(i) Discuss passive and active uptake of nutrients by plants. (ii) Discuss the principles of breaking seed dormancy. [1996/30m/3b]
Explain in brief: (i) What will be the effect of excessive use of fertilizers on the soil? (ii) What will be the effect of excessive irrigation on the production of crop? [1995/20m/6a]
4.2] Soil-water-plant relationship
27 questions
Explain the factors that affect the amount of soil water available for plants. [2026/20m/4b]
What do you understand by water transport in xylem? Explain the Cohesion-Tension theory. [2025/20m/4a]
Briefly explain the Soil-Plant-Atmosphere Continuum (SPAC). How are rooting characteristics related to the moisture extraction pattern from the soil? [2024/10m/2c]
Give the classification of soil water. Briefly discuss soil moisture availability with respect to soil type. [2023/10m/150w/1d]
Give an account of stomate anatomy and cytology. Write down the effect of light, water deficit, CO₂ concentration and temperature on stomatal movement along with the underlying mechanism. [2023/20m/4b]
Define matric potential, osmotic potential and turgor potential, and explain their interrelationships with water potential. [2022/10m/150w/1e]
Describe the mechanisms involved in absorption of water in plants. Explain the factors affecting the water absorption rate in plants. [2021/20m/4c]
“The rate of transpiration governs the growth of a plant.” Justify the statement with reasoning for how transpiration is influenced by the environment. [2019/10m/150w/5e]
What do you mean by Soil-Plant-Atmosphere Continuum (SPAC)? Describe the different soil moisture constants. [2018/15m/4c]
Define ‘evapotranspiration’. How is it affected by various factors? Briefly discuss the passive absorption of water by plants. [2017/20m/6a]
How is water absorbed by land plants? Explain various external conditions affecting water absorption by roots. [2016/12.5m/2d]
Differentiate between transpiration and guttation. Why permanent wilting takes place? [2016/12.5m/4d]
Explain the phenomenon of passive absorption and give the factors affecting the rate of absorption of water. [2016/12.5m/6d]
What are the fundamental difference between transpiration and guttation? In a winter morning, water droplets might be noticed on some plant leaves. How could it be ascertained whether the water droplets were those of dew drops or guttation water? [2014/10m/150w/5a]
Differentiate between incipient wilting, temporary wilting and permanent wilting. Classify different types of droughts and mention how are they related to each other. [2014/10m/150w/5d]
Give an account of different types of water present in soil. [2014/12.5m/6c]
Mechanism of translocation of water from roots to leaves. [2013/12.5m/200w/6a]
Water potential of plant cells. [2013/12.5m/200w/7a]
What are plant antitranspirants? Discuss their applications giving suitable examples. [2011/15m/150w/2d]
Outline the mechanism of opening and closing of stomata with reference to K⁺ ion transport mechanism. [2010/15m/3d]
Describe the diffusion phenomenon involved in water relation of crops. [2007/20m/200w/1d]
Define diffusion. What factors influence the rate of diffusion? [2006/20m/200w/1b]
Water economy in potato. [2005/15m/8d]
Define transpiration. What are the factors affecting transpiration? [2004/20m/2a]
Osmotic pressure cell sap. [2003/15m/4a]
Explain in brief: (i) What will be the effect of excessive use of fertilizers on the soil? (ii) What will be the effect of excessive irrigation on the production of crop? [1995/20m/6a]
Water economy. [1995/7.5m/8h]
4.3] Enzymes and plant pigments
15 questions
Explain the biosynthetic pathways of chlorophylls and carotenoids in plants. How do environmental factors influence plant pigments? [2026/20m/6b]
Explain the properties and functions of enzymes in plants. [2024/10m/150w/5a]
Enlist various photosynthetic pigments. Give a detailed account of chlorophyll synthesis along with the enzymes involved in the process. Also mention the role of carotenoids in photosynthesis. [2023/20m/7a]
What are enzymes? Describe “Key-lock theory” with respect to mode of enzyme action. [2021/15m/6a]
Define enzyme. Give a note on the factors affecting the rate of enzymic activities in plants. [2018/10m/150w/1e]
Explain the effect of concentration of enzyme on its activity. Give different methods for regulating the enzymic activity. [2016/12.5m/7d]
What are Enzymes? Write the properties and factors affecting enzyme’s activity. [2015/10m/150w/1c]
Show full reactions where (i) Alcohol dehydrogenase, (ii) Nitrate reductase, (iii) Glucokinase and (iv) Succinate dehydrogenase are involved, therewith mentioning respective co-factor, co-enzyme, prosthetic group etc., if so required. [2014/10m/150w/5c]
Plant enzymes and their role in the vital activities of plants. [2011/15m/150w/4d]
What are ENZYMES? Discuss their mode of action in plant system? [2007/20m/2a]
Plant pigments. [2003/15m/4b]
Write briefly on:- (i) Carotenoids, (ii) C₄ plants [?], (iii) Glycolysis and (iv) Osmosis and Turgor. [1999/20m/200w/1d]
Write about the classification of enzymes based on their role and how is their action regulated. [1999/20m/2a]
Plant pigments. [1998/7.5m/4g]
What are the factors that influence enzymatic reactions? Explain with suitable examples. [1996/20m/200w/1a]
4.4] Photosynthesis
24 questions
List the reactions of Calvin Cycle and Hatch-Slack Cycle for CO₂ fixation in plants along with enzymes involved. [2023/20m/7b]
Discuss photorespiration. What is the relationship between photorespiration and photosynthesis? [2022/20m/7b]
Differentiate between the following: (i) Plant hormones and Synthetic plant-growth regulators (ii) C₃ and C₄ plants. [2020/10m/150w/5a]
Explain C₃, C₄ and CAM mechanism in plants and their importance in changing climatic conditions. [2018/10m/150w/5b]
What is photophosphorylation? Distinguish between cyclic and non-cyclic photophosphorylation. Give schematic structure of both the pathways. [2017/20m/6b]
What do you mean by C₃, C₄ and CAM mechanisms? [2015/10m/150w/1e]
Name the process by which carbohydrates are synthesized in plants. Narrate its mechanism. [2015/12.5m/7b]
Write short note on Hill reaction. Prove that O₂ evolved during photosynthesis comes from water and not from CO₂. [2014/10m/150w/5e]
The relative responses of photosynthesis in C₃ and C₄ plants to temperature and CO₂ concentration. [2013/10m/150w/5b]
Distinguish between the C₃ and C₄ mechanisms of photosynthesis and discuss the biological significance of C₄ cycle. [2011/15m/150w/3d]
Define oxidative phosphorylation and photo-phosphorylation. Distinguish between non-cyclic and cyclic electron transport process of photosynthesis. [2010/20m/200w/6c]
Describe the specific features of C4 plants. How they differ from C3 type? [2007/20m/200w/1b]
Respiration and photosynthesis. [2006/20m/200w/4b]
Define photosynthesis. Discuss its dark and light reactions. [2005/20m/5a]
Define photosynthesis in plants. Narrate the sequential processes occurring therein with an illustration. [2004/20m/3c]
Describe the role of photo-morphogenesis in plants and explain the influence of light on biomass accumulation in plants. [2001/20m/3b]
Describe the part played by chlorophyll, carbon dioxide and light in the synthesis of carbohydrates. [2000/20m/200w/1d]
Write briefly on:- (i) Carotenoids, (ii) C₄ plants [?], (iii) Glycolysis and (iv) Osmosis and Turgor. [1999/20m/200w/1d]
What are dark and light reactions in photosynthesis? [1998/20m/200w/2b]
Differentiate in detail between photosynthesis and respiration processes. [1998/20m/200w/2c]
Describe translocation of Photosynthates. [1997/20m/200w/5d]
Comment upon fossil energy, fixation of energy and biomass. [1996/30m/2b]
Photorespiration. [1996/10m/4c]
Discuss the relative photosynthetic efficiency of C-3 and C-4 plants. [1995/20m/200w/1c]
4.5] Respiration
10 questions
Describe the process of anaerobic respiration and explain the factors affecting respiration. [2024/20m/6a]
Explain oxidative decarboxylation citing suitable example. [2016/12.5m/3a]
Explain the connection between anaerobic and aerobic respiration. [2016/10m/150w/5b]
Define respiration and state why is this process essential for plants. [2015/12.5m/6c]
What is aerobic respiration? Describe the Krebs cycle reactions and discuss its significance in plant life. [2012/20m/250w/6a]
Define oxidative phosphorylation and photo-phosphorylation. Distinguish between non-cyclic and cyclic electron transport process of photosynthesis. [2010/20m/200w/6c]
Respiration and photosynthesis. [2006/20m/200w/4b]
Non-aerobic respiration. [2000/15m/8d]
Differentiate in detail between photosynthesis and respiration processes. [1998/20m/200w/2c]
ATP. [1996/10m/4b]
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6 questions
How do plants absorb nitrogen from the environment? Describe the mechanism of nitrate assimilation and synthesis of amino acids in plants. [2025/10m/150w/5a]
Briefly discuss the pathways of carbohydrate metabolism in plants. [2023/10m/7c]
Give a detailed account of sucrose metabolism in plants. [2022/10m/150w/5a]
Differentiate between symbiotic and asymbiotic nitrogen fixation. How does symbiotic nitrogen fixation take place in crop plants? [2017/10m/7c]
Give evidences supporting translocation of organic solutes in phloem. Explain Ringing experiment. [2016/12.5m/3b]
Delineate the carbohydrate metabolism in crop plants. [2009/20m/200w/4b]
4.7] Growth and development; photoperiodism and vernalization
23 questions
Differentiate plant growth and development. Explain the different phases of growth in plants and also discuss the various methods of growth measurement and growth analysis. [2025/20m/7b]
What is phytochrome? Discuss its two forms and differentiate them. [2024/20m/8b]
What do you understand by vernalization? Describe its practical application in crops. [2021/20m/6c]
What is photoperiodism? Write at least one example of shortday plant, longday plant and day neutral plant. [2015/12.5m/4a]
What is meant by ‘sigmoid’ growth curve? Draw and describe a sigmoid growth curve citing its different phases. [2014/10m/150w/5b]
Define vernalization. How vernalization is activated in plants? Briefly discuss its importance in agriculture. [2014/12.5m/6a]
What is photoinsensitivity? Discuss its significance in crop production. [2011/15m/150w/1d]
The physiological processes mediated by phytochrome pigment. [2010/15m/150w/1d]
The influence of various spectrums of light on root development, stem growth and the maturity of fruit in fruit plants. [2010/15m/150w/8c]
Describe the photoperiodism in crop plants. [2007/20m/3b]
Short-day and Long-day plants. [2007/20m/4b]
Photoperiodism. [2006/20m/200w/8c]
Discuss about photoperiodism and vernalization. [2005/20m/5b]
Discuss the role of photoperiodism and vernalization. [2003/20m/5c]
Explain the role of vernalization in crop production. [2001/20m/200w/1d]
Describe the role of photo-morphogenesis in plants and explain the influence of light on biomass accumulation in plants. [2001/20m/3b]
Vernalization. [2000/15m/4c]
Write about the phytochrome and its distribution in plants. [1999/20m/200w/1b]
Short day plants and Long day plants. [1998/7.5m/4e]
Define growth. Describe main stages of growth in plants. [1997/30m/3a]
Explain the internal and external factors that favour following. [?]. [1996/20m/200w/1d]
Vernalisation. [1995/10m/4b]
Senescence. [1995/10m/4c]
4.8] Plant growth substances and their role in crop production
23 questions
What do you mean by new generation plant growth regulators? Enlist the different new generation plant growth regulators and also discuss their role in mitigating abiotic stresses. [2025/20m/8a]
Enlist the role of auxins in agriculture, with suitable examples. [2023/10m/150w/5c]
Define biotic stress in plants. Explain the role of salicylic acid in a plant’s response to biotic stress. [2022/10m/6c]
Differentiate between the following: (i) Plant hormones and Synthetic plant-growth regulators (ii) C₃ and C₄ plants. [2020/10m/150w/5a]
Define plant growth regulators. Elaborate their applications with suitable examples. [2020/15m/7c]
Explain the role of plant growth substances in the various developmental stages of a plant with special reference to horticultural crops. [2019/20m/3a]
Define auxins and explain their role in crop life cycles. Also, discuss the uses of auxins in agriculture. [2018/20m/6a]
What are plant growth regulators? How do they differ from phytohormones? Indicate the applications of plant growth regulators in agriculture. [2017/10m/150w/5a]
Role of gibberellins in plant growth and development. [2013/12.5m/200w/8b]
What are phytohormones? Describe the physiological roles of auxins and gibberellins in plants. [2012/12m/150w/1d]
Describe role of Auxins in the growth and development of crop plants. [2007/20m/200w/5b]
What are auxins? Mention their characteristics and practical use in agriculture. [2006/20m/200w/2a]
Define and discuss plant growth regulators and their use in agriculture. [2002/20m/3c]
Define plant growth regulators. Classify them according to their mode of action, and discuss their use in horticulture. [2001/20m/3a]
Apical dominance has great significance in floriculture and landscape gardening. [2001/15m/4d]
What are auxins? Give their mode of action and explain their importance with reference to horticulture in India. [2000/20m/200w/5c]
Mention the different plant growth substances and write about the purposes for which they are utilised. [1999/20m/3a]
What are Gibberellins? How do they differ from auxins? Explain applications of GAS in agriculture and horticulture crops. [1998/20m/200w/3a]
Compare between plant growth inhibitors and plant growth retardants with examples. [1998/20m/200w/3b]
Use of cultar in mango cultivation. [1998/7.5m/8g]
Explain the Growth Promoters and Growth Retardants. [1997/20m/200w/1c]
What is the practical value of apical dominance? [1995/20m/3a]
What is the place of origin, translocation, effect on plant growth and mode of disintegration of natural auxins in plants? [1995/20m/3b]
4.9] Seed development, germination and dormancy
13 questions
Explain the different types of seed dormancy. What are the factors that are responsible for dormancy in seeds? [2026/10m/7c]
Define seed viability. Describe in brief the metabolic aspects of seed germination. [2021/10m/150w/5a]
Define dormant and hard seeds. Describe the physiological basis of seed dormancy along with methods to overcome this problem. [2019/10m/150w/1b]
What do you understand by seed dormancy? Discuss the reasons for seed dormancy. Also, describe the various methods for breaking seed dormancy. [2018/15m/6c]
What is stress physiology? Write the physiology of seed germination and development. [2015/12.5m/3d]
What are orthodox and re-calcitrant seeds? What are the different phases associated with germination of orthodox seed. [2010/15m/150w/5a]
What is dormancy of seed? How it is managed? [2007/20m/2c]
Endospermic and Non-endospermic seed. [2007/20m/4a]
Germination and dormancy. [2003/20m/8a]
Explain about the causes of seed dormancy. Suggest methods of breaking seed dormancy. [1999/20m/2c]
Imbibition. [1999/10m/4c]
Seed dormancy. [1998/7.5m/4h]
(i) Discuss passive and active uptake of nutrients by plants. (ii) Discuss the principles of breaking seed dormancy. [1996/30m/3b]
4.10] Stress physiology
13 questions
Discuss the role of osmoprotectants in plants with reference to salt and water stress. [2026/10m/150w/5e]
How does salinity affect the growth and photosynthesis in plants? Elucidate the avoidance mechanisms of salt stress by plants. [2025/10m/6c]
What do you mean by new generation plant growth regulators? Enlist the different new generation plant growth regulators and also discuss their role in mitigating abiotic stresses. [2025/20m/8a]
Define water stress. Discuss the effects of water stress on anatomical and physiological changes in plant growth. Also discuss soil and weather based plant water stress indicators. [2024/20m/7a]
What is plant physiological stress? Describe morphological and physiochemical changes taking place in plants under drought condition. [2021/15m/6b]
Give a brief account of the effects of drought and salt stress on growth and development of crops. [2020/10m/150w/5b]
Discuss the effects of water stress on plant growth and development. Describe plant borne mechanisms to escape from drought and stress situations. [2018/15m/6b]
What is stress physiology? Write the physiology of seed germination and development. [2015/12.5m/3d]
Differentiate between incipient wilting, temporary wilting and permanent wilting. Classify different types of droughts and mention how are they related to each other. [2014/10m/150w/5d]
Define the term stress. Give an account on how water deficit is created inside the tissue system in relation to injury and tolerance mechanism. [2012/15m/200w/2d]
Differentiate stress from strain. Give an account of morphological adaptive changes in plants to survive drought situation. [2010/20m/200w/6b]
Temperature induced injuries in fruits and vegetables. [2010/15m/150w/8d]
Describe the temperature-induced injuries in fruits, vegetables and flower crops. Explain the strategies by which these injuries can be avoided. [2001/20m/3c]
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Last updated: 30 October 2026